1. Field of the Invention
The present invention relates to a duplexer and a communication apparatus for use in a microwave band, for example, a mobile phone or the like.
2. Description of the Related Art
A known duplexer comprising dielectric coaxial resonators has a structure shown in FIG. 5.
This duplexer includes a transmitting-side which comprises a band-elimination filter having four xcex/4-type dielectric coaxial resonators R1 through R4 and a receiving-side which comprises a band-pass filter having four xcex/4-type dielectric coaxial resonators R5 through R8.
Here, xe2x80x9ca xcex/4-type dielectric coaxial resonatorxe2x80x9d means a dielectric coaxial resonator adapted to resonate at a frequency and having a length which is a quarter wavelength at that frequency. To obtain such dielectric coaxial resonator, one end surface of the dielectric coaxial resonator is made electrically open-circuited (i.e., the open end surface), and the other end surface of the dielectric coaxial resonator is made electrically short-circuited (i.e., the short end surface).
The open end surfaces of the dielectric coaxial resonators R1 through R4 constituting the transmitting-side filter are arranged side by side substantially on the left-half side of a base substrate 2 and the open end surfaces of the dielectric coaxial resonators R5 through R8 constituting the receiving-side filter are arranged side by side substantially on the right-half of the same in such a manner that the open end surfaces of both sides are disposed in the same direction and their axes are in parallel to each other. Capacitors C, air-core coils L, and the coupling substrate 3 are disposed on the side of the open end surfaces of the resonators R1 through R8 provided on the base substrate 2; and the resonators R1 through R8 are coupled by the coupling elements such as the capacitors C, the air-core coils L, and capacitors provided on the base substrate 2 and the coupling substrate 3, through a connection terminal 4 connected to an inner conductor of each resonator. The resonators R1, R4, R5, and R8, which are input-output units, are connected to a transmission terminal 6, which is an input-output terminal on the transmitting side formed on the base substrate 2, a reception terminal 7, which is an input-output terminal on the receiving side, and an antenna terminal 8 sharing the input-output terminals of the transmitting side and the receiving side, directly or through a coupling element.
Recently, small, lightweight, and thin types of radio communication apparatus such as mobile phones have been rapidly spreading. With this trend, a duplexer which is used in this type of radio communication apparatus, is required to be small, lightweight, and thin, so that the size of a dielectric coaxial resonator used in a duplexer, recently 4 mm square or 3 mm square, is becoming smaller year by year, to as small as 2 mm square.
However, in the above described duplexer, the open end surfaces of all the dielectric coaxial resonators are on the same side. When a smaller dielectric coaxial resonator is used to achieve miniaturization of a duplexer, since the smaller the size of the dielectric coaxial resonator, the smaller the area on which coupling elements can be mounted for coupling the resonators, it is impossible to dispose a coupling element having a specified configuration or a specified value.
Specifically, when the size of the dielectric coaxial resonator is modified from 3 mm square to 2 mm square, the dimension of the available area for arranging the dielectric coaxial resonators side by side is reduced by a third, and the distance between the resonators is reduced by a third, so that it is impossible to use an air-core coil, a coupling substrate and the like, which are used in a 3 mm-square resonator, in a duplexer formed of 2 mm-square resonators. In contrast, when the air-core coil, the coupling substrate, and the like, are made smaller corresponding to the distance between the resonators, it is impossible to obtain inductance and capacitance of a desired value or desired characteristics. Worse, variations in the characteristics increase. In addition, in the above conventional duplexer, the reception terminal, the transmission terminal, and the antenna terminal are formed close to one side of the base substrate, so that when it is miniaturized, the distances between the terminals are shorter; thereby, signal leakage, due, for example to capacitive coupling between terminals or an actual arc caused by dielectric breakdown between terminals, may occur between the transmission terminal and the antenna terminal or between the reception terminal and the antenna terminal, so that sufficient isolation cannot be obtained.
In other words, in the structure of the above described duplexer, when smaller dielectric coaxial resonators are used to achieve miniaturization of the duplexer, the characteristics can greatly deteriorate and the characteristic variations can increase.
To overcome the above described problems, preferred embodiments of the present invention provide a duplexer and a communication apparatus, which are small, low-cost, and have satisfactory characteristics.
One preferred embodiment of the present invention provides a duplexer comprising: xcex/4-type dielectric coaxial resonators constituting a transmitting-side filter; xcex/4-type dielectric coaxial resonators constituting a receiving-side filter; and coupling elements for coupling said resonators; wherein the dielectric coaxial resonators constituting the transmitting-side filter and the dielectric coaxial resonators constituting the receiving-side filter are placed in parallel; and the open end surfaces of the dielectric coaxial resonators constituting the transmitting-side filter and the open end surfaces of the dielectric coaxial resonators constituting the receiving-side filter are disposed in opposite directions.
Another preferred embodiment of the present invention provides a duplexer comprising: xcex/4-type dielectric coaxial resonators constituting a transmitting-side filter; xcex/4-type dielectric coaxial resonators constituting a receiving-side filter; and coupling elements for coupling said resonators; wherein the respective dielectric coaxial resonators are placed side by side in such a manner that at least one of the dielectric coaxial resonators constituting either one of filters is disposed between the dielectric coaxial resonators constituting the other of the filters; and the open end surfaces of the dielectric coaxial resonators constituting the transmitting-side filter and the open end surfaces of the dielectric coaxial resonators constituting the receiving-side filter are disposed in opposite directions.
Still another preferred embodiment of the present invention provides a duplexer comprising: xcex/4-type dielectric coaxial resonators constituting a transmitting-side filter; xcex/4-type dielectric coaxial resonators constituting a receiving-side filter; and coupling elements for coupling said resonators; wherein the respective ones of the dielectric coaxial resonators constituting the transmitting-side filter and the respective ones of the dielectric coaxial resonators constituting the receiving-side filter are alternately disposed side by side; and the open end surfaces of the dielectric coaxial resonators constituting the transmitting-side filter and the open end surfaces of the dielectric coaxial resonators constituting the receiving-side filter are disposed in opposite directions.
Yet another preferred embodiment of the present invention provides a communication apparatus comprising the above described duplexer.
In the duplexer having the above-described structure, the respective dielectric coaxial resonators are disposed in parallel in such a manner that the open end surfaces of the dielectric coaxial resonators forming the transmitting-side filter and the open end surfaces of the dielectric coaxial resonators forming the receiving-side filter are disposed in opposite directions. This arrangement permits coupling elements connected to the dielectric coaxial resonators of the transmitting-side filter and coupling elements connected to the dielectric coaxial resonators of the receiving-side filter to be respectively disposed on the opposite sides, with respect to the resonator length direction of the dielectric coaxial resonators, so that the width and the area for mounting the coupling elements can be substantially expanded. Thus, even if smaller dielectric coaxial resonators are used, coupling elements having the same configuration as those used in the conventional large-size dielectric coaxial resonators can be used. Or coupling elements having satisfactory characteristics, and having fewer variations in the characteristics, can be used. In this case, changing the order in which the dielectric coaxial resonators are disposed permits coupling elements having more appropriate configurations and characteristics to be used.
Disposition of the dielectric coaxial resonators constituting the transmitting-side filter and the dielectric coaxial resonators constituting the receiving-side filter in alternating directions permits the dimensions of the dielectric coaxial resonators forming the duplexer to be even, and longer, and permits the use of coupling elements having the most appropriate configurations and characteristics.
In other words, flexibility is increased as to the sizes of the coupling elements, and it thereby becomes possible to use coupling elements having better characteristics and commonality.
In addition, since the antenna terminal can be provided on the side opposite to the side on which the transmission terminal and the reception terminal are provided, and the distances between the terminals can be kept sufficiently large, occurrence of signal-hops between the transmission terminal and the antenna terminal or between the reception terminal and the antenna terminal can be prevented so as to ensure sufficient isolation between the transmitting-side filter and the receiving-side filter.
Furthermore, since the communication apparatus according to the present invention is formed by including the duplexer having the above characteristics, it can be smaller and low-cost, and can have satisfactory characteristics.
Other features and advantages of the present invention will become apparent from the following description of embodiments of the invention which refers to the accompanying drawings.